1. Field of the Invention
This invention relates to a semiconductor treatment system and a method for exchanging and treating substrates such as semiconductor wafers and LCD substrates.
2. Description of the Related Art
In the manufacturing process of a semiconductor device or an LCD (liquid crystal display) device, a resist coating system or a resist developing system is used. Such a system performs wafer exchange in a treatment section with the use of a transfer robot having two forked arms. FIGS. 1A to 1H and FIGS. 2A to 2H show conventional procedures for wafer exchange.
FIGS. 1A to 1H show a procedure of exchanging, in a treatment section, a wafer W1 placed on a work table, which has been treated, with a wafer W2 placed on a lower arm 4, which is to be treated next.
Referring to FIG. 1A, an upper arm 6 is raised, together with the lower arm 4, to a level at which the arm 6 can be inserted under the wafer W1 which has been treated, and then the upper arm 6 is advanced to the wafer W1. Thereafter, a support portion 2 supporting the arms 4 and 6 is moved upward to cause the arm 6 to raise the wafer W1 (FIG. 1B). The upper arm 6 is then retreated, with the wafer W1 kept thereon (FIGS. 1C, 1D).
When the upper arm 6 is returned to the initial or retreat position, the support portion 2 is further raised to position the lower arm 4 higher than the work table (FIG. 1E). At this level, the lower arm 4 with the wafer W2 to be treated next is advanced toward the table (FIG. 1F). When the lower arm 4 has reached a position above the table, the support portion 2 is moved downward to transfer the wafer W2 from the arm 4 to the table (FIG. 1G). Subsequently, the lower arm 4 is retreated to the initial position (FIG. 1H).
FIGS. 2A to 2H show a procedure of exchanging a wafer W1 placed on the work table, which has already been treated, with a wafer W2 placed on the upper arm 6, which is to be treated next.
The lower arm 4 is raised, together with the upper arm 6, to a level at which the lower arm 4 can be inserted under the treated wafer W1, and then the lower arm 4 is advanced to the wafer W1 (FIG. 2A). Thereafter, the support portion 2 is moved upward to cause the arm 4 to raise the wafer W1 (FIG. 2B). The lower arm 4 is then retreated (FIGS. 2C).
Subsequently, the support portion 2 is lowered slightly, and the upper arm 6 with the wafer W2 placed thereon is advanced toward the work table (FIG. 2E). When the upper arm 6 has reached a position above the table, the support portion 2 is moved downward to transfer the wafer W2 from the arm 6 to the table (FIGS. 2F, 2G). Following transfer of the wafer W2, the upper arm 6 is retreated to the initial position (FIG. 2H).
FIG. 3 is a timing chart, useful in explaining the timing of wafer exchange. The left side portion of the chart indicates the timing of the wafer exchange shown in FIGS. 1A to 1H, while the right side portion indicates that of the wafer exchange shown in FIGS. 2A to 2H. As is evident from FIG. 3, the lower and upper arms can operate independent of each other, and the operations of the arms are performed on a continuous basis. In other words, after the unloading operation of the treated wafer W1 is finished, the loading operation of the wafer W2 to be treated is subsequently initiated. Thus, the time period required for wafer exchange is the sum of the time periods necessary to perform the unloading and loading operations.
If the time required for wafer exchange is long, it inevitably reduces the throughput. Further, if this is the case, then, a wafer to be subsequently treated will be adversely affected by the heat of a wafer having been treated or by the heat of the atmosphere, and accurate control of the temperature of the wafer will become difficult. For example, in a resist coating system, the longer the time period required for wafer exchange is, the higher the temperature of a wafer, which has been set to a predetermined value in a cooling section, is liable to become, due to the ambient temperature. As a result, the uniformity of the thickness of a resist film formed in a resist coating section is lowered.
The above disadvantage appears particularly in the case of treating a large substrate such as an LCD substrate. This is because long stroke arms must be used to unload and load large substrates, and the time periods required for the unloading and loading are inevitably long.